Mazia's group is continuing the analysis of how the mitotic apparatus is constructed. Techniques devised for microscopical analysis of the formation of a bipolar mitotic apparatus will be employed to follow the processes of chromosome engagement, the formation of centrioles, and the recruitment of microtubules into the mitotic apparatus. Microtubules organizing centers will be isolated from cells and used in studies in how tubulin, in vitro, generates structures. Fusion of cells in different stages of the cell cycle will be used to analyze the interaction of different organelles and molecules during the cell cycle. Wilt's laboratory will continue to study the stability of histone mRNA in cleaving sea urchin eggs, and also to study the stability of the mRNA after it has been microinjected into living Xenopus oocytes. New studies on the role of cell division in control of histone mRNA synthesis will be conducted. Studies using 2D gel electrophoresis on the number and kinds of non-histone proteins present in chromatin of embryo blastomeres will be continued. Studies on the regulation of myogenesis are continuing in Dr. Strohman's laboratory. The effects of the drugs tetrodotoxin and diazepam on the ultrastructure of the differentiating myoblasts will be carried out. Furthermore, the effects of these same two drugs, both of which cause atrophy in myofibrils, in vitro, on the synthesis and accumulation of myosin mRNA will be studied. Experiments on the turnover of the myosin component of the myofilament will be conducted using new and improved methods for isolation of myofilaments from cultured cells.